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  • 1
    Electronic Resource
    Electronic Resource
    Evidence for vitamin D-independent active calcium absorption in newborn piglets (1993)
    Springer
    Calcified tissue international 52 (1993), S. 305-309 
    Details
    ISSN: 1432-0827
    Keywords: Calcitriol ; Ca2+ absorption ; Vitamin D receptor ; Piglets ; Pseudo vitamin D deficiency ; Rickets
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary The role of 1,25-dihydroxycholecalciferol (calcitriol) for intestinal calcium (Ca2+) absorption was studied in newborn (〈1 week old) and weaned piglets (〉6 weeks old). In both groups, normal piglets and piglets suffering from inherited pseudo vitamin D-deficiency rickets, type I (PVDRI) were used. In this inherited disorder, renal production of calcitriol is absent. Plasma samples were assayed for calcitriol and total Ca, and dissociation constants (Kd) and maximum binding capacities (Bmax) of intestinal calcitriol receptors were determined under equilibrium conditions at 4°C. Unidirectional Ca2+-flux rates were measured across stripped duodenal mucosae in Ussing chambers in the absence of electrochemical gradients. The plasma calcitriol concentrations of neonatal (26.5±7.1 pg/ml, n=11; $$\bar x$$ ± SEM) and weaned PVDRI piglets (18.8±5.7 pg/ml, n=8)were unphysiologically low and differed significantly from control animals (83.6±14.8 pg/ml, n=8, and 86.9±9.6 pg/ml, n=11, respectively). However, newborn PVDRI piglets had normal plasma Ca levels at least during the first days of life. They became hypocalcemic and developed clinical symptoms of rickets during the following weeks. In newborn PVDRI and control piglets, Bmax was significantly lower (84±28 fmol/mg protein and 127±55 fmol/mg protein, n=9, respectively) than in weaned piglets (741±82 fmol/mg protein, n=9, and 778±121 fmol/mg protein, n=8, respectively). Significant net Ca2+-fluxes were found in both newborn PVDRI and control piglets (88.8±25.1 nmol · cm-2 · h-1, n=6, and 86.5±10.5 nmol · cm−2 · h−1,n=9, respectively). However, active net Ca2+ absorption was completely absent in weaned PVDRI piglets. These results indicate the presence of vitamin D-independent mechanisms for active intestinal Ca2+ absorption during early postnatal life in pigs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00296656
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  • 2
    Electronic Resource
    Electronic Resource
    Analysis of parotid and mixed saliva in Roe deer (Capreolus capreolus L.) (1998)
    Springer
    Journal of comparative physiology 168 (1998), S. 257-264 
    Details
    ISSN: 1432-136X
    Keywords: Key words Roe deer ; Salivary proteins ; Tannin-binding
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract In ruminants, different functions have been ascribed to the different salivary glands according to the feeding type. In this context, possible adaptations of salivary functions were investigated regarding the secretion of various proteins by different types of salivary glands. To yield uncontaminated parotid saliva in large quantities, a non-surgical method has been developed. Parotid gland secretions were collected via endoscopic placement of guide wires into each parotid duct, which were subsequently used for placement of collection catheters. Salivary flow was stimulated by intra-glandular administration of the parasympathomimetic compound pilocarpine-hydrochloride into the parotid gland. Mixed saliva (excluding parotid saliva) was collected into sterile tubes by normal outflow during the sampling of parotid saliva. The total flow volume, flow rate and the content of proteins as well as of several ions (Na+, K+, Ca2+, inorganic phosphate) of both types of saliva were measured in sheep, fallow deer and roe deer. Roe deer secreted the highest amount of total salivary proteins relative to body mass [mg/kg body mass] and the highest relative volume [ml/10 min/kg body mass], both in parotid and mixed saliva, of all ruminant species examined. Additionally, the protein profile and the tannin-binding properties of parotid and mixed saliva in roe deer were investigated. Parotid saliva bound almost twice as much tannin as mixed saliva, underlining the importance of yielding uncontaminated parotid saliva for tannin-binding studies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003600050144
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  • 3
    Electronic Resource
    Electronic Resource
    Mechanisms of phosphate uptake into brush-border membrane vesicles from goat jejunum (1996)
    Springer
    Journal of comparative physiology 166 (1996), S. 230-240 
    Details
    ISSN: 1432-136X
    Keywords: Phosphate transport ; Jejunum ; Calcitriol ; Goats
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract This study concerns the uptake of inorganic phosphate into brush-border membrane vesicles prepared from jejunal tissues of either control or Ca-and/or P-depleted goats. The brush-border membrane vesicles showed a time-dependent accumulation of inorganic phosphate with a typical overshoot phenomenon in the presence of an inwardly directed Na+ gradient. The Na+-dependent inorganic phosphate uptake was completely inhibited by application of 5 mmol·l-1 sodium arsenate. Half-maximal stimulation of inorganic phosphate uptake into brush-border membrane vesicles was found with Na+ concentrations in the order of 5 mmol·l-1. Inorganic phosphate accumulation was not affected by a K+ diffusion potential (inside negative), suggesting an electroneutral transport process. Stoichiometry suggested an interaction of two or more Na ions with one inorganic phosphate ion at pH 7.4. Na+-dependent inorganic phosphate uptake into jejunal brush-border membrane vesicles from normal goats as a function of inorganic phosphate concentration showed typical Michaelis-Menten kinetic with V max=0.42±0.08 nmol·mg-1 protein per 15 s-1 and K m=0.03±0.01 mmol·l-1 (n=4, x ±SEM). Long-term P depletion had no effect on these kinetic parameters. Increased plasma calcitriol concentrations in Ca-depleted goats, however, were associated with significant increases of V max by 35–80%, irrespective of the level of P intake. In the presence of an inwardly directed Na+ gradient inorganic phosphate uptake was significantly stimulated by almost 60% when the external pH was decreased to 5.4 (pHout/pHin=5.4/7.4). The proton gradient had no effect on inorganic phosphate uptake in absence of Na+. In summary, in goats Na+ and calcitriol-dependent mechanisms are involved in inorganic phosphate transport into jejunal brush-border membrane vesicles which can be stimulated by protons.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00263987
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